I have a RAID-5. I'm trying to replace a failing drive in Disk Utility GUI. I added a new drive as a spare, then did "Remove Component" for the failing drive. How do I tell it to actually use the spare (write all the parity data, etc)?
I tried re-adding, because I got nervous...
$ sudo mdadm /dev/md127 --re-add /dev/sdd
mdadm: --re-add for /dev/sdd to /dev/md127 is not possible